Concerning Grayling's observation that his parents and grandparent's etc. had to have meet in order for him to be born, he admits on page 80 of The God Argument that this is 'a retrospective observation', which amounts to admitting that his grandparent example isn't analogous to the independently specified complexity of cosmic fine-tuning.

Here's a YouTube video of our discussion of the Cosmological Argument:

Peter Byrom kindly gave me permission to reproduce here an e-mail he sent in to Justin Brierly's Unbelievable following the broadcast:

Dear Justin,

Very glad you were
able to get A.C. Grayling onto your show, though it is odd that he appears to
have suddenly re-discovered an interest in theistic arguments: When you invited
him to debate William Lane Craig in 2011, he dismissed the whole discussion of
arguments for God as "an empty prospect", but now apparently they're
worthy of a whole new book called "The God Argument"!

But onto the
discussion itself: it was astonishing to hear a Professor, who charges £18,000
tuition a year, exhibiting such fallacious and sloppy reasoning. I counted at
least six invocations of the genetic fallacy: where Grayling tried to undermine
inferences to God, agent causation (and even the principle of causation itself)
by repeatedly claiming that humans are psychologically and historically
pre-disposed towards them. So what? This does nothing to address the argument.

In fact, when
invited to respond to Peter S William's critique for why you do not need an
explanation of an explanation, Grayling had nothing else to offer other than
the genetic fallacy! I encourage listeners therefore to do an
experiment: listen to the show again, but omit every instance where
Grayling says something like "it's very natural for us humans to infer
this, because..." or "that's a very egocentric way of seeing things",
and see what you're left with!

As for the specific
arguments:

Teleological: Grayling admitted he would draw a design inference
from Peter S William's analogy of the cash machine... so why not the
fine-tuning of the universe? The most Grayling could do was fixate upon the
alternative analogy of the contingent events which led up to his birth, but
this was simply not an example of specified complexity: the existence of AC
Grayling as opposed to some different human life, does not conform to an
independently given pattern in the way that the existence of human life as
opposed to a lifeless universe does. This blog post by Jonathan Mclatchie
goes into brilliant detail on why Grayling is confused here, and I recommend it
to all listeners: http://www.evolutionnews.org/2013/04/ac_graylings_co071041.html

Furthermore,
Grayling was content to say "we exist, that's a fact, and that's just the
way it is"! Apart from this being a disturbingly incurious statement,
Grayling then made a completely illogical leap: claiming that "we exist,
that's just a fact, therefore it's due to chance". But how does that
follow? The same would be true of our existence if the explanation were physical
necessity or design. So Grayling was simply plucking his preferred explanation
out of thin air.

Grayling also
doesn't appear to be up to speed on the problems with multiverse models (lookup
the criticisms by Roger Penrose especially). But even if there were an
infinity of all possible outcomes in a multiverse, Grayling would have to face
the problem that there would be an infinity of universes where somebody enters
the correct PIN code for his bank account by sheer chance, and an infinity of
universes where the words in Grayling's books arise out of no intelligent
cause! ;-)

Cosmological: Grayling persistently side-stepped the inference to a
necessary being in the most school-boyish manner: he seemed to think he could
undermine the idea of a necessary first cause of the universe by calling it
"Fred", but that is mere semantics! What matters is not what you call
something, but the properties of what that being actually is. An englishman
will say "dog", a frenchman will say "chien", but they're
still referring to the same thing (it's called "ontology",
Professor)!

Grayling then
contradicted himself on multiple counts: he said it was meaningless to invoke
an uncaused first cause, then offered naturalistic versions of "uncaused
first causes" (even going further to offer logically contradictory
"self-caustion"); He said reality may be different to what we
can comprehend, then complained God was incomprehensible; he said we
humans cannot get our heads round things not being caused, then complained that
God would need to be caused! He demanded an explanation for God, but not for
the universe; he even went so far as to describe the question "why is
there something rather than nothing" as a meaningless question, and
compared it to asking "why is 3 greater than 2"... but the irony is
that there IS a meaningful answer to that question: NECESSARILY EXISTENT
mathematical axioms!

Moral: This one was simplest (and most simplistic) of all.
Grayling said that facts about human flourishing serve as a basis for objective
moral values, but this is nonsense: those descriptive facts do nothing to prescribe
the obligation that humans ought to flourish! It was also telling that
he had no response to the "horn-splitting" Euthyphro Dilemma
resolution... as if he'd never even heard of it.

In all, Grayling's
arguments were horrendous, yet he has an unnerving rhetorical talent for
dressing up sheer lack of curiosity as some kind of sophisticated, academic
virtue. Do not be fooled!